The 24-year-old defenseman, who has 25 points (five goals, 20 assists) and a minus-16 rating in 62 games for the Ducks this season, can become a restricted free agent after the 2019-20 season.
"Brandon is a young, offensive-minded defenseman who can play the up-tempo style we are looking to play," Sabres general manager Jason Botterill said. "He's a right-shot defenseman that brings additional playoff experience to our club."
The Sabres (29-24-8), who are six points behind the Carolina Hurricanes for the second wild card into the Stanley Cup Playoffs from the Eastern Conference, have allowed 3.07 goals per game this season, which is ranked 17th in the NHL.
The Ducks (24-29-9) are eight points behind the Colorado Avalanche for the second wild card in the West.
Selected by the Ducks in the second round (No. 55) of the 2014 NHL Draft, Montour has 63 points (16 goals, 47 assists) in 169 regular-season games, and eight points, all assists, in 21 games in the Stanley Cup Playoffs.
The draft pick will come from either San Jose or St. Louis (both owned by Buffalo) based on the final order of selection in the 2019 NHL Draft.
Guhle (6-foot-2, 196 pounds) has five assists in 23 games with Buffalo and 27 points (five goals, 22 assists) in 50 games with Rochester of the American Hockey League.
"Brendan Guhle is an excellent skater who is ready to take the next step in his career," said Ducks GM and coach Bob Murray. "Adding Guhle and a first-round pick is an important step as we retool our team moving forward. We also thank Brandon Montour for his efforts and wish him the best of luck in Buffalo."
